Method and apparatus for document identification

ABSTRACT

A currency identification system comprises at least two laterally displaced scanheads, one or more laterally moveable scanheads, or at least two laterally displaced sensors of a linear scanhead. The scanheads or sensors are positioned so as to permit scanning along at least two segments on a first side of a bill. The scanheads or sensors are capable of detecting characteristic information from the bill along the segments and generating corresponding output signals representing variations in the detected characteristic information from which scanned patterns of characteristic information may be generated. The system also comprises a pattern generator for generating at least one scanned pattern from the output signals, the scanned pattern representing analog variations in the characteristic information along a segment of the bill. The system also comprises a memory for storing at least one master pattern associated with each genuine bill. The system further comprises a signal processor for performing a pattern comparison wherein at least one of the scanned patterns or portions thereof is compared with at least one of the master patterns or portions thereof. The signal processor generates an indication of the identity of the bill based on the pattern comparison when the bill is one that the system is capable of identifying.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.08/287,882 filed Aug. 9, 1994 for a "Method and Apparatus for DocumentIdentification." U.S. patent application Ser. No. 08/287,882 is acontinuation-in-part of U.S. patent application Ser. No. 08/127,334filed Sep. 27, 1993, and issued as U.S. Pat. No. 5,467,405, for a"Method and Apparatus for Currency Discrimination and Counting," acontinuation-in-part of abandoned U.S. patent application Ser. No.08/219,093 filed Mar. 29, 1994, for a "Currency Discriminator andAuthenticator," and a continuation-in-part of U.S. patent applicationSer. No. 08/207,592 filed on Mar. 8, 1994, and issued as U.S. Pat. No.5,467,406 for a "Method and Apparatus for Currency Discrimination." U.S.patent application Ser. No. 08/127,334 is a continuation of U.S. patentapplication Ser. No. 07/885,648, filed on May 19, 1992, and issued asU.S. Pat. No. 5,295,196, for a "Method and Apparatus for CurrencyDiscrimination and Counting," which is a continuation-in-part ofabandoned U.S. patent application Ser. No. 07/475,111, filed Feb. 5,1990, for a "Method and Apparatus for Currency Discrimination andCounting." U.S. patent application Ser. No. 08/219,093 is acontinuation-in-part of U.S. patent application Ser. No. 08/127,334filed Sep. 27, 1993, for a "Method and Apparatus for CurrencyDiscrimination and Counting", which is a continuation of U.S. patentapplication Ser. No. 07/885,648, filed on May 19, 1992, and issued asU.S. Pat. No. 5,295,196, for a "Method and Apparatus for CurrencyDiscrimination and Counting," which is a continuation-in-part ofabandoned U.S. patent application Ser. No. 07/475,111, filed Feb. 5,1990, for a "Method and Apparatus for Currency Discrimination andCounting." U.S. patent application Ser. No. 08/207,592 is acontinuation-in-part of U.S. patent application Ser. No. 08/127,334filed Sep. 27, 1993, for a "Method and Apparatus for CurrencyDiscrimination and Counting", which is a continuation of U.S. patentapplication Ser. No. 07/885,648, filed on May 19, 1992, and issued asU.S. Pat. No. 5,295,196, for a "Method and Apparatus for CurrencyDiscrimination and Counting," which is a continuation-in-part ofabandoned U.S. patent application Ser. No. 07/475,111, filed Feb. 5,1990, for a "Method and Apparatus for Currency Discrimination andCounting."

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to document identification.More specifically, the present invention relates to an apparatus andmethod for discriminating among a plurality of document types such ascurrency bills of different denominations and/or from differentcountries.

2. Background

A variety of techniques and apparatus have been used to satisfy therequirements of automated currency handling systems. At the lower end ofsophistication in this area of technology are systems capable ofhandling only a specific type of currency, such as a specific dollardenomination, while rejecting all other currency types. At the upper endare complex systems which are capable of identifying and discriminatingamong and automatically counting multiple currency denominations.

Currency discrimination systems typically employ either magnetic sensingor optical sensing for discriminating among different currencydenominations. Magnetic sensing is based on detecting the presence orabsence of magnetic ink in portions of the printed indicia on thecurrency by using magnetic sensors, usually ferrite core-based sensors,and using the detected magnetic signals, after undergoing analog ordigital processing, as the basis for currency discrimination. A varietyof currency characteristics can be measured using magnetic sensing.These include detection of patterns of changes in magnetic flux,patterns of vertical grid lines in the portrait area of bills, thepresence of a security thread, total amount of magnetizable material ofa bill, patterns from sensing the strength of magnetic fields along abill, and other patterns and counts from scanning different portions ofthe bill such as the area in which the denomination is written out.

The more commonly used optical sensing techniques, on the other hand,are based on detecting and analyzing variations in light reflectance ortransmissivity characteristics occurring when a currency bill isilluminated and scanned by a strip of focused light. The subsequentcurrency discrimination is based on the comparison of sensed opticalcharacteristics with prestored parameters for different currencydenominations, while accounting for adequate tolerances reflectingdifferences among individual bills of a given denomination. A variety ofcurrency characteristics can be measured using optical sensing. Theseinclude detection of a bill's density, color, length and thickness, thepresence of a security thread and holes, and other patterns ofreflectance and transmission. Color detection techniques may employcolor filters, colored lamps, and/or dichroic beamsplitters.

In addition to magnetic and optical sensing, other techniques ofdetecting characteristic information of currency include electricalconductivity sensing, capacitive sensing (such as for watermarks,security threads, thickness, and various dielectric properties) andmechanical sensing (such as for size, limpness, and thickness).

A major obstacle in implementing automated currency discriminationsystems is obtaining an optimum compromise between the criteria used toadequately define the characteristic pattern for a particular currencydenomination, the time required to analyze test data and compare it topredefined parameters in order to identify the currency bill underscrutiny, and the rate at which successive currency bills may bemechanically fed through and scanned. Even with the use ofmicroprocessors for processing the test data resulting from the scanningof a bill, a finite amount of time is required for acquiring samples andfor the process of comparing the test data to stored parameters toidentify the denomination of the bill.

Recent currency discriminating systems rely on comparisons between ascanned pattern obtained from a subject bill and sets of stored masterpatterns for the various denominations among which the system isdesigned to discriminate. For example, it has been found that scanningU.S. bills of different denominations along a central portion thereofprovides scanning patterns sufficiently divergent to enable accuratediscrimination between different denominations. Such a discriminationdevice is disclosed in U.S. Pat. No. 5,295,196. However, currencies ofother countries can differ from U.S. currency and from each other in anumber of ways. For example, while all denominations of U.S. currenciesare the same size, in many other countries currencies vary in size bydenomination. Furthermore, there is a wide variety of bill sizes amongdifferent countries. In addition to size, the color of currency can varyby country and by denomination. Likewise, many other characteristics mayvary between bills from different countries and of differentdenominations.

As a result of the wide variety of currencies used throughout the world,a discrimination system designed to handle bills of one countrygenerally can not handle bills from another country. Likewise, themethod of discriminating bills of different denominations of one countrymay not be appropriate for use in discriminating bills of differentdenominations of another country. For example, scanning for a givencharacteristic pattern along a certain portion of bills of one country,such as optical reflectance about the central portion of U.S. bills, maynot provide optimal discrimination properties for bills of anothercountry, such as German marks.

Furthermore, there is a distinct need for an identification system whichis capable of accepting bills of a number of currency systems, that is,a system capable of accepting a number of bill-types. For example, abank in Europe may need to process on a regular basis French, British,German, Dutch, etc. currency, each having a number of differentdenomination values.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved methodand apparatus for identifying documents.

It is an object of the present invention to provide an improved methodand apparatus for discriminating among currency bills comprising aplurality of currency denominations.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of efficientlydiscriminating among bills of several currency denominations at a highspeed and with a high degree of accuracy.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of efficientlydiscriminating currencies from a number of different countries.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of scanning a document suchas a currency bill along two or more laterally displaced segments tothereby identify the document.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of scanning a documentalong two or more laterally displaced segments by using two or morelaterally displaced scanheads.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of scanning a documentalong two or more laterally displaced segments by using two or morelaterally displaced sensors of a linear array scanhead.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of scanning a documentalong two or more laterally displaced segments by using one or morelaterally moveable scanheads.

It is another object of this invention to provide an improved method andapparatus of the above kind wherein the above scanheads or sensorsretrieve optical reflectance information from a document under test anduse such reflectance information to determine the identity of thedocument.

It is another object of this invention to provide an improved method andapparatus of the above kind which identifies a document by comparing oneor more scanned patterns generated by scanning a document under testwith one or more scanheads or one or more sensors and comparing thescanned pattern or patterns with one or more master patterns associatedwith genuine documents.

It is another object of this invention to provide an improved method andapparatus of the above kind which identifies a document by determiningthe size of the document.

It is another object of this invention to provide an improved method andapparatus of the above kind which identifies a document by determiningthe color of the document.

It is another object of this invention to provide an improved method andapparatus of the above kind which identifies a document based on acombination of size information and scanned/master pattern comparison.

It is another object of this invention to provide an improved method andapparatus of the above kind which identifies a document based on acombination of color information and scanned/master pattern comparison.

It is another object of this invention to provide an improved method andapparatus of the above kind which identifies a document based on acombination of size information, color information, and scanned/masterpattern comparison.

It is another object of this invention to provide an improved method andapparatus of the above kind in which only selected ones of a number ofscanheads or sensors are activated to scan a document.

It is another object of this invention to provide an improved method andapparatus of the above kind in which scanned patterns are generated onlyfrom the output or data derived therefrom of selected ones of a numberof scanheads or sensors which are activated to scan a document.

It is another object of this invention to provide an improved method andapparatus of the above kind in which the selection of one or more of anumber of scanheads or sensors to scan a document is based on sizeinformation.

It is another object of this invention to provide an improved method andapparatus of the above kind in which the selection of one or more of anumber of scanheads or sensors to scan a document is based on colorinformation.

It is another object of this invention to provide an improved method andapparatus of the above kind in which the lateral positioning of one ormore moveable scanheads is based on size and/or color informationdetected from the document.

It is another object of this invention to provide an improved method andapparatus of the above kind in which the selection of the output or dataderived therefrom of one or more of a number of scanheads or sensors forthe generation of scanned patterns is based on size information.

It is another object of this invention to provide an improved method andapparatus of the above kind in which the selection of the output or dataderived therefrom of one or more of a number of scanheads or sensors forthe generation of scanned patterns is based on color information.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of scanning either side orboth sides of a document.

It is another object of this invention to provide an improved method andapparatus of the above kind in which the amount of information that mustbe processed is reduced by tailoring the areas from which scannedpatterns are derived, such reduction being based on pre-scan informationdetected from a document such as the size and/or color of a document tobe scanned.

It is another object of this invention to provide an improved method andapparatus of the above kind in which the amount of information that mustbe processed is reduced by tailoring the data which must be assembledinto one or more scanned patterns, such reduction being based oninformation detected from a document during the scanning process itself,the information detected during the scanning process itself including,for example, size and/or color information.

It is another object of this invention to provide an improved method andapparatus of the above kind in which size and/or color informationdetected from a document is used to generate a preliminary set ofpotentially matching documents and in which one or more scanned patternsgenerated from a document are compared with master patterns chosen fromthe preliminary set.

It is another object of this invention to provide an improved method andapparatus of the above kind in which a document to be scanned istransported past one or more scanheads in a centered or justified manneralong a transport path.

It is another object of this invention to provide an improved method andapparatus of the above kind in which a document to be scanned istransported past one or more scanheads along a transport path and inwhich one or more sensors separate from the one or more scanheads areused to determine the lateral positioning of the document within thetransport path.

It is another object of this invention to provide an improved method andapparatus of the above kind in which a document to be scanned istransported past one or more scanheads along a transport path and inwhich the lateral positioning of the document within the transport pathis determined by analyzing of output of one or more scanheads.

It is another object of this invention to provide an improved method andapparatus of the above kind in which a document to be scanned istransported past one or more scanheads along a transport path and inwhich the skew of the document is determined by analyzing of output ofone or more scanheads or analyzing the output of one or more separatesensors.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of accepting documents fedeither face up or face down.

It is another object of this invention to provide an improved method andapparatus of the above kind which is capable of accepting documents fedin either the forward or reverse direction, i.e., top edge first or topedge last.

A related object of the present invention is to provide such an improvedcurrency discrimination and counting apparatus which is compact,economical, and has uncomplicated construction and operation.

Briefly, in accordance with the present invention, the objectivesenumerated above are achieved by scanning a document along one or moresegments, generating one or more scanned patterns therefrom, andcomparing the one or more scanned patterns to one or more masterpatterns associated with scans along corresponding segments of genuinedocuments. A preferred embodiment of the present invention involves atechnique based on the optical sensing of reflectance characteristicsobtained by illuminating and scanning a document such as a currency billalong an appropriately selected segment or segments of a document. Lightreflected from the bill as it is optically scanned is detected and usedas an analog representation of the variation in the dark and lightcontent of the printed pattern or indicia on the bill surface.

A series of such detected reflectance signals are obtained by samplingand digitally processing, under microprocessor control, the reflectedlight at a plurality of predefined sample points as the bill is movedacross the illuminated strip. Accordingly, a fixed number of reflectancesamples is obtained across the note. The data samples obtained for abill scan are subjected to digital processing, including a normalizingprocess to deaccentuate variations due to contrast fluctuations in theprinted pattern or indicia existing on the surface of the bill beingscanned. The normalized reflectance data represent a characteristicpattern that is fairly unique for a given bill identity and incorporatessufficient distinguishing features between characteristic patterns fordifferent bill-types so as to accurately differentiate therebetween.

By using the above approach, a series of master characteristic patternsare generated and stored using standard bills for each denomination ofcurrency that is to be detected. The "standard" bills used to generatethe master characteristic patterns are preferably bills that areslightly used bills. According to a preferred embodiment, two or fourcharacteristic patterns are generated and stored within system memoryfor each detectable bill-type. The stored patterns correspond,respectively, to optical scans performed on one or both sides of a billalong "forward" and "reverse" directions relative to the pattern printedon the bill. For bills which produce significant pattern changes whenshifted slightly to the left or right, such as the $10 bill in U.S.currency, it is preferred to store two patterns for each of the"forward" and "reverse directions, each pair of patterns for the samedirection represent two scan areas that are slightly displaced from eachother along the lateral dimension of the bill. Preferably, the documentidentification system of this invention is adapted to identify differentdenominations of a plurality of currency systems. Accordingly, a masterset of different characteristic patterns is stored within the systemmemory for subsequent correlation purposes.

According to the correlation technique of this invention, the patterngenerated by scanning a bill under test and processing the sampled datais compared with each of the prestored characteristic patterns within apreliminary set (to be described below) to generate, for eachcomparison, a correlation number representing the extent of similaritybetween corresponding ones of the plurality of data samples for thecompared patterns. Bill identification is based on designating thescanned bill as belonging to the bill-type corresponding to the storedcharacteristic pattern for which the correlation number resulting frompattern comparison is determined to be the highest. The possibility of ascanned bill having its identity mischaracterized following thecomparison of characteristic patterns is significantly reduced bydefining a bi-level threshold of correlation that must be satisfied fora "positive" call to be made.

In essence, the present invention utilizes an optical sensing andcorrelation technique for positively identifying any of a plurality ofdifferent bill-types regardless of whether the bill is scanned along the"forward" or "reverse" directions. Likewise in a preferred embodiment ofthe present invention, the system is capable of identifying any of aplurality of different bill-types regardless of whether the bill is fedinto the system with a "face up" or "face down" orientation. Faceorientation can be accommodated by storing master patterns scanned fromboth sides of genuine documents, using a system having one or morescanheads on a single side of a document transport path, and comparingscanned patterns to master patterns retrieved from both sides of genuinedocuments. Alternatively, scanheads may be placed on both sides of adocument transport path, scanned patterns retrieved from respectivesides can be compared to master patterns from both sides or masterpatterns from corresponding sides where face orientation can bedetermined. Additionally, a cross check can be performed so that theidentity determined by a match of patterns from one side of a documentis consistent with the identity indicated by comparing patterns from theother side of the document. For both one-sided and two-sided scanheadsystems, where the face orientation of a document can be determinedbefore patterns are compared, scanned patterns from one side of adocument can be compared only to master patterns retrieved from acorresponding side. Similar methods can be employed for accommodatingdocuments fed in forward and reverse directions.

In a preferred embodiment, the invention is particularly adapted to beimplemented with a system programmed to track each identified currencyidentity so as to conveniently present aggregate totals for bills thathave been identified at the end of a scan run. A preferred embodimentincorporates an abbreviated curved transport path for accepting currencybills that are to be counted and transporting the bills about theirnarrow dimension across a scanhead located downstream of the curved pathand onto a conventional stacking station where sensed and counted billsare collected. In a preferred embodiment, a scanhead of the presentinvention operates in conjunction with an optical encoder which isadapted to initiate the capture of a predefined number of reflectancedata samples when a bill (and, thus, the indicia or pattern printedthereupon) moves across a coherent strip of light focused by thescanhead.

In a preferred embodiment, a scanhead of the present invention uses apair of light-emitting diodes ("LEDs") to focus a coherent light stripof predefined dimensions and having a normalized distribution of lightintensity across the illuminated area. The LEDs are angularly disposedand focus the desired strip of light onto the narrow dimension of a billpositioned flat across the scanning surface of the scanhead. Aphotodetector detects light reflected from the bill. The sampling of thephotodetector output is controlled by the optical encoder to obtain thedesired reflectance samples. Initiation of sampling is based upondetection of the edge of a bill.

The above described techniques and apparatus as tailored to scanningU.S. currency are more fully disclosed in U.S. Pat. No. 5,295,196, for a"Method and Apparatus for Currency Discrimination and Counting"incorporated herein in its entirety.

In adapting the currency discriminating method and apparatus disclosedin U.S. Pat. No. 5,295,196 to optimize the scanning of currencies fromcountries other than the United States, it is first noted that while ithas been found that scanning along the central portion of the green sideof U.S. bills provides good patterns to discriminate between thedifferent U.S. denominations, foreign bills may require scanning alongsegments located in locations other than the center and the desirableareas to scan bills can vary from bill-type to bill-type. For example,it may be determined that it is desirable to scan German marks in theforward direction along a segment 1 inch (2.54 cm) to the left of centeralong the top face of a bill while it may be desirable to scan Britishpounds along a segment 1.5 inches (3.81 cm) to the right of center. Toprovide a system capable of scanning along a plurality of laterallydisplaced segments, the present invention utilizes either a plurality oflaterally displaced stationary scanheads, one or more laterally moveablescanheads, or a linear array scanhead having a plurality of laterallydisplaced sensors. In a preferred embodiment, the scanheads or sensorsare arranged in a symmetrical manner about the center of document to bescanned. Such a symmetrical arrangement aids in providing a system whichis capable of accepting bills fed in both the forward and reversedirections.

Additionally, while all denominations of U.S. currency have the samesize, currencies from other countries may vary in size from country tocountry as well as from denomination to denomination for currency fromthe same country. In a preferred embodiment of the present invention,variance in size is accommodated by incorporating means for determiningthe size of a document. These size determining means may include sensorsseparate from the scanheads or scanning sensors discussed above oralternatively, in some preferred embodiments of the present invention,may include the scanheads or scanning sensors discussed above which areused for the retrieval of scanned characteristic patterns. Based on thesize information retrieved from a bill, selected scanheads may beactivated, laterally moveable scanheads may be appropriately positionedand activated, and/or selected sensors in a linear array scanhead may beactivated to permit scanning along appropriate segments of a bill basedon its size. Alternatively, all scanheads or scanning sensors may beactivated and the output of appropriately positioned scanheads orscanning sensors may be processed to generate scanned patterns based onthe size of a bill. Furthermore, based on the size of a bill, apreliminary determination can be made as to which of a plurality ofgenuine bill-types a bill under test may potentially match. Based onsuch a preliminary determination, the comparison of generated scannedpatterns can be limited to only master patterns associated withbill-types chosen from the preliminary set of potentially matchingbills.

Likewise, the transport mechanism which transports documents to bescanned past the above described scanheads may be designed to transportdocuments in a centered manner, left or right justified manner, in anon-controlled lateral positioned manner, in a non-skewed manner, or ina skewed manner. Sensors separate and distinct from the above describedscanheads or the above described scanheads themselves may be used todetermine the lateral positioning of transported bills and/or theirdegree of skew. Based on a determination of the laterally positioning ofa bill and/or its skew, appropriately positioned scanheads or scanningsensors may be activated or laterally moveable scanheads may beappropriately positioned and activated or the output from appropriatelypositioned scanheads or scanning sensors may be processed to generatescanned patterns based on the lateral positioning and/or skew of thebill.

Additionally, while all denominations of U.S. currency have the samecolors (a "green" side and a "black" side), currencies from othercountries may vary in color from country to country as well as fromdenomination to denomination for currency from the same country. In apreferred embodiment of the present invention, variance in color isaccommodated by incorporating means for determining the color of adocument. These color determining means may include sensors separatefrom the scanheads or sensors discussed above or alternatively, in somepreferred embodiments of the present invention, may include theappropriately modified scanheads or sensors discussed above which areused for the retrieval of scanned characteristic patterns. For example,colored filters may be placed in front of the above described scanheadsor sensors. Based on the color information retrieved from a bill,selected scanheads may be activated, laterally moveable scanheads may beappropriately positioned and activated, and/or selected sensors in alinear array scanhead may be activated to permit scanning alongappropriate segments of a bill based on its color. Alternatively, allscanheads or scanning sensors may be activated and the output ofappropriately positioned scanheads or scanning sensors may be processedto generate scanned patterns based on the color of a bill. Furthermore,based on the color of a bill, a preliminary determination can be made asto which of a plurality of genuine bill-types a bill under test maypotentially match. Based on such a preliminary determination, thecomparison of generated scanned patterns can be limited to only masterpatterns associated with bill-types chosen from the preliminary set ofpotentially matching bills.

In a preferred embodiment of the present invention, both color and sizeinformation may be utilized as described above.

In a preferred embodiment of the present invention, scanheads arepositioned on both sides of a document transport path so as to permitscanning of either or both sides of a document.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description in conjunction with thedrawings in which:

FIG. 1 is a functional block diagram illustrating a currencydiscriminating system having a single scanhead;

FIG. 2A is a diagrammatic perspective illustration of the successiveareas scanned during the traversing movement of a single bill across anoptical sensor according to a preferred embodiment of the presentinvention;

FIG. 2B is a perspective view of a bill and a preferred area to beoptically scanned on the bill;

FIG. 2C is a diagrammatic side elevation view of the scan area to beoptically scanned on a bill according to a preferred embodiment of thepresent invention;

FIG. 3A is a block diagram illustrating a preferred circuit arrangementfor processing and correlating reflectance data according to the opticalsensing and counting technique of this invention;

FIG. 3B is a block diagram illustrating a circuit arrangement forproducing a reset signal;

FIG. 4 is a top view of a bill and size determining sensors according toa preferred embodiment of the present invention;

FIG. 5 is a top view of a bill illustrating multiple areas to beoptically scanned on a bill according to a preferred embodiment of thepresent invention;

FIG. 6A is a graph illustrating a scanned pattern which is offset from acorresponding master pattern;

FIG. 6B is a graph illustrating the same patterns of FIG. 6A after thescanned pattern is shifted relative to the master pattern;

FIG. 7 is a side elevation of a multiple scanhead arrangement accordingto a preferred embodiment of the present invention;

FIG. 8 is a side elevation of a multiple scanhead arrangement accordingto another preferred embodiment of the present invention;

FIG. 9 is a side elevation of a multiple scanhead arrangement accordingto another preferred embodiment of the present invention;

FIG. 10 is a side elevation of a multiple scanhead arrangement accordingto another preferred embodiment of the present invention;

FIG. 11 is a top view of a staggered scanhead arrangement according to apreferred embodiment of the present invention;

FIG. 12A is a top view of a linear array scanhead according to apreferred embodiment of the present invention illustrating a bill beingfed in a centered fashion;

FIG. 12B is a side view of a linear array scanhead according to apreferred embodiment of the present invention illustrating a bill beingfed in a centered fashion;

FIG. 13 is a top view of a linear array scanhead according to anotherpreferred embodiment of the present invention illustrating a bill beingfed in a non-centered fashion;

FIG. 14 is a top view of a linear array scanhead according to anotherpreferred embodiment of the present invention illustrating a bill beingfed in a skewed fashion; and

FIGS. 15A and 15B are a flowchart of the operation of a currencydiscrimination system according to a preferred embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to a preferred embodiment of the present invention, multiplescanheads per side are used to scan a bill. Nonetheless, beforeexplaining such a multiple head scanner, the operation of a scannerhaving a single scanhead is first described. In particular, a currencydiscrimination system adapted to U.S. currency is described inconnection with FIGS. 1-3. Subsequently, modifications to such adiscrimination system will be described in obtaining a currencydiscrimination system in accordance with the present invention.Furthermore, while the preferred embodiments below entail the scanningof currency bills, the system of the present invention is applicable toother documents as well. For example, the system of the presentinvention may be employed in conjunction with stock certificates, bonds,and postage and food stamps.

Referring now to FIG. 1, there is shown a functional block diagramillustrating a currency discriminating system having a single scanhead.The system 10 includes a bill accepting station 12 where stacks ofcurrency bills that need to be identified and counted are positioned.Accepted bills are acted upon by a bill separating station 14 whichfunctions to pick out or separate one bill at a time for beingsequentially relayed by a bill transport mechanism 16, according to aprecisely predetermined transport path, across scanhead 18 where thecurrency denomination of the bill is scanned and identified. Scanhead 18is an optical scanhead that scans for characteristic information from ascanned bill 17 which is used to identify the denomination of the bill.The scanned bill 17 is then transported to a bill stacking station 20where bills so processed are stacked for subsequent removal.

The optical scanhead 18 of FIG. 1 comprises at least one light source 22directing a beam of coherent light downwardly onto the bill transportpath so as to illuminate a substantially rectangular light strip 24 upona currency bill 17 positioned on the transport path below the scanhead18. Light reflected off the illuminated strip 24 is sensed by aphotodetector 26 positioned directly above the strip. The analog outputof photodetector 26 is converted into a digital signal by means of ananalog-to-digital (ADC) convertor unit 28 whose output is fed as adigital input to a central processing unit (CPU) 30.

While scanhead 18 of FIG. 1 is an optical scanhead, it should beunderstood that it may be designed to detect a variety of characteristicinformation from currency bills. Additionally, the scanhead may employ avariety of detection means such as magnetic, optical, electricalconductivity, and capacitive sensors. Use of such sensors is discussedin more detail U.S. patent application Ser. No. 08/219,093 filed on Mar.29, 1994 for a "Currency Discriminator and Authenticator" andincorporated herein by reference.

Referring again to FIG. 1, the bill transport path is defined in such away that the transport mechanism 16 moves currency bills with the narrowdimension of the bills being parallel to the transport path and the scandirection. Alternatively, the system 10 may be designed to scan billsalong their long dimension or along a skewed dimension. As a bill 17moves on the transport path on the scanhead 18, the coherent light strip24 effectively scans the bill across the narrow dimension of the bill.As depicted, the transport path is so arranged that a currency bill 17is scanned by scanhead 18 approximately about the central section of thebill along its narrow dimension, as shown in FIG. 1. The scanhead 18functions to detect light reflected from the bill as it moves across theilluminated light strip 24 and to provide an analog representation ofthe variation in light so reflected which, in turn, represents thevariation in the dark and light content of the printed pattern orindicia on the surface of the bill. This variation in light reflectedfrom the narrow dimension scanning of the bills serves as a measure fordistinguishing, with a high degree of confidence, among a plurality ofcurrency denominations which the system of this invention is programmedto handle.

A series of such detected reflectance signals are obtained across thenarrow dimension of the bill, or across a selected segment thereof, andthe resulting analog signals are digitized under control of the CPU 30to yield a fixed number of digital reflectance data samples. The datasamples are then subjected to a digitizing process which includes anormalizing routine for processing the sampled data for improvedcorrelation and for smoothing out variations due to contrastfluctuations in the printed pattern existing on the bill surface. Thenormalized reflectance data so digitized represents a characteristicpattern that is fairly unique for a given bill denomination and providessufficient distinguishing features among characteristic patterns fordifferent currency denominations. This process is more fully explainedin U.S. patent application Ser. No. 07/885,648, filed on May 19, 1992,now issued as U.S. Pat. No. 5,295,196 for a "Method and Apparatus forCurrency Discrimination and Counting," which is incorporated herein byreference in its entirety.

In order to ensure strict correspondence between reflectance samplesobtained by narrow dimension scanning of successive bills, theinitiation of the reflectance sampling process is preferably controlledthrough the CPU 30 by means of an optical encoder 32 which is linked tothe bill transport mechanism 16 and precisely tracks the physicalmovement of the bill 17 across the scanhead 18. More specifically, theoptical encoder 32 is linked to the rotary motion of the drive motorwhich generates the movement imparted to the bill as it is relayed alongthe transport path. In addition, the mechanics of the feed mechanism(not shown, see U.S. Pat. No. 5,295,196 referred to above) ensure thatpositive contact is maintained between the bill and the transport path,particularly when the bill is being scanned by scanhead 18. Under theseconditions, the optical encoder 32 is capable of precisely tracking themovement of the bill 17 relative to the light strip 24 generated by thescanhead 18 by monitoring the rotary motion of the drive motor.

The output of photodetector 26 is monitored by the CPU 30 to initiallydetect the presence of the bill underneath the scanhead 18 and,subsequently, to detect the starting point of the printed pattern on thebill, as represented by the thin borderline 17A which typically enclosesthe printed indicia on currency bills. Once the borderline 17A has beendetected, the optical encoder 32 is used to control the timing andnumber of reflectance samples that are obtained from the output of thephotodetector 26 as the bill 17 moves across the scanhead 18 and isscanned along its narrow dimension.

The use of the optical encoder 32 for controlling the sampling processrelative to the physical movement of a bill 17 across the scanhead 18 isalso advantageous in that the encoder 32 can be used to provide apredetermined delay following detection of the borderline prior toinitiation of samples. The encoder delay can be adjusted in such a waythat the bill 17 is scanned only across those segments along its narrowdimension which contain the most distinguishable printed indiciarelative to the different currency denominations.

In the case of U.S. currency, for instance, it has been determined thatthe central, approximately two-inch (approximately 5 cm) portion ofcurrency bills, as scanned across the central section of the narrowdimension of the bill, provides sufficient data for distinguishing amongthe various U.S. currency denominations on the basis of the correlationtechnique disclosed in U.S. Pat. No. 5,295,196 referred to above.Accordingly, the optical encoder can be used to control the scanningprocess so that reflectance samples are taken for a set period of timeand only after a certain period of time has elapsed since the borderline17A has been detected, thereby restricting the scanning to the desiredcentral portion of the narrow dimension of the bill.

FIGS. 2A-2C illustrate the scanning process of scanhead 20 in moredetail. Referring to FIG. 2B, as a bill 17 is advanced in a directionparallel to the narrow edges of the bill, scanning via a wide slit inthe scanhead 18 is effected along a segment S of the central portion ofthe bill 17. This segment S begins a fixed distance D inboard of theborderline 17A. As the bill 17 traverses the scanhead 18, a strip s ofthe segment S is always illuminated, and the photodetector 26 produces acontinuous output signal which is proportional to the intensity of thelight reflected from the illuminated strip s at any given instant. Thisoutput is sampled at intervals controlled by the encoder, so that thesampling intervals are precisely synchronized with the movement of thebill across the scanhead 18.

As illustrated in FIGS. 2A and 2C, it is preferred that the samplingintervals be selected so that the strips s that are illuminated forsuccessive samples overlap one another. The odd-numbered andeven-numbered sample strips have been separated in FIGS. 2A and 2C tomore clearly illustrate this overlap. For example, the first and secondstrips s1 and s2 overlap each other, the second and third strips s2 ands3 overlap each other, and so on. Each adjacent pair of strips overlapeach other. For U.S. currency, this is accomplished by sampling stripsthat are 0.050 inch (0.127 cm) wide at 0.029 inch (0.074 cm) intervals,along a segment S that is 1.83 inch (4.65 cm) long (64 samples).

The optical sensing and correlation technique is based upon using theabove process to generate a series of stored intensity signal patternsusing genuine bills for each denomination of currency that is to bedetected. According to a preferred embodiment, two or four sets ofmaster intensity signal samples are generated and stored within systemmemory, preferably in the form of an EPROM 34 (see FIG. 1), for eachdetectable currency denomination. The sets of master intensity signalsamples for each bill are generated from optical scans, performed on thegreen surface of the bill and taken along both the "forward" and"reverse" directions relative to the pattern printed on the bill.Alternatively, the optical scanning may be performed on the black sideof U.S. currency bills or on either surface of bills from othercountries. Additionally, the optical scanning may be performed on bothsides of a bill, for example, by placing a scanhead on each side of thebill transport path as described in more detail in co-pending U.S.patent application Ser. No. 08/207,592 filed Mar. 8, 1994, for a "Methodand Apparatus for Currency Discrimination" and incorporated herein byreference.

In adapting this technique to U.S. currency, for example, sets of storedintensity signal samples are generated and stored for seven differentdenominations of U.S. currency, i.e., $1, $2, $5, $10, $20, $50 and$100. For bills which produce significant pattern changes when shiftedslightly to the left or right, such as the $2 and the $10 bill in U.S.currency, it is preferred to store two patterns for each of the"forward" and "reverse" directions, each pair of patterns for the samedirection represent two scan areas that are slightly displaced from eachother along the long dimension of the bill. Accordingly, a set of 18different master characteristic patterns is stored within the systemmemory for subsequent correlation purposes (four master patterns for the$2 and the $10 bill and two master patterns for each of the otherdenominations). Once the master patterns have been stored, the patterngenerated by scanning a bill under test is compared by the CPU 30 witheach of the 18 master patterns of stored intensity signal samples togenerate, for each comparison, a correlation number representing theextent of correlation, i.e., similarity between corresponding ones ofthe plurality of data samples, for the sets of data being compared.

The CPU 30 is programmed to identify the denomination of the scannedbill as corresponding to the set of stored intensity signal samples forwhich the correlation number resulting from pattern comparison is foundto be the highest. In order to preclude the possibility ofmischaracterizing the denomination of a scanned bill, as well as toreduce the possibility of spurious notes being identified as belongingto a valid denomination, a bi-level threshold of correlation is used asthe basis for making a "positive" call. Such a method is disclosed inU.S. Pat. No. 5,295,196 referred to above. If a "positive" call can notbe made for a scanned bill, an error signal is generated.

Using the above sensing and correlation approach, the CPU 30 isprogrammed to count the number of bills belonging to a particularcurrency denomination as part of a given set of bills that have beenscanned for a given scan batch, and to determine the aggregate total ofthe currency amount represented by the bills scanned during a scanbatch. The CPU 30 is also linked to an output unit 36 (FIG. 1) which isadapted to provide a display of the number of bills counted, thebreakdown of the bills in terms of currency denomination, and theaggregate total of the currency value represented by counted bills. Theoutput unit 36 can also be adapted to provide a print-out of thedisplayed information in a desired format.

Referring now to FIG. 3A, there is shown a representation, in blockdiagram form, of a preferred circuit arrangement for processing andcorrelating reflectance data according to the system of this invention.As shown therein, the CPU 30 accepts and processes a variety of inputsignals including those from the optical encoder 32, the photodetector26 and a memory unit 38, which can be an erasable programmable read onlymemory (EPROM). The memory unit 38 has stored within it the correlationprogram on the basis of which patterns are generated and test patternscompared with stored master programs in order to identify thedenomination of test currency. A crystal 40 serves as the time base forthe CPU 30, which is also provided with an external reference voltageV_(REF) on the basis of which peak detection of sensed reflectance datais performed.

The CPU 30 also accepts a timer reset signal from a reset unit 44 which,as shown in FIG. 3B, accepts the output voltage from the photodetector26 and compares it, by means of a threshold detector 44A, relative to apre-set voltage threshold, typically 5.0 volts, to provide a resetsignal which goes "high" when a reflectance value corresponding to thepresence of paper is sensed. More specifically, reflectance sampling isbased on the premise that no portion of the illuminated light strip (24in FIG. 1) is reflected to the photodetector in the absence of a billpositioned below the scanhead. Under these conditions, the output of thephotodetector represents a "dark" or "zero" level reading. Thephotodetector output changes to a "white" reading, typically set to havea value of about 5.0 volts, when the edge of a bill first becomespositioned below the scanhead and falls under the light strip 24. Whenthis occurs, the reset unit 44 provides a "high" signal to the CPU 30and marks the initiation of the scanning procedure.

The machine-direction dimension, that is, the dimension parallel to thedirection of bill movement, of the illuminated strip of light producedby the light sources within the scanhead is set to be relatively smallfor the initial stage of the scan when the thin borderline is beingdetected. The use of the narrow slit increases the sensitivity withwhich the reflected light is detected and allows minute variations inthe "gray" level reflected off the bill surface to be sensed. This isimportant in ensuring that the thin borderline of the pattern, i.e., thestarting point of the printed pattern on the bill, is accuratelydetected. Once the borderline has been detected, subsequent reflectancesampling is performed on the basis of a relatively wider light strip inorder to completely scan across the narrow dimension of the bill andobtain the desired number of samples, at a rapid rate. The use of awider slit for the actual sampling also smooths out the outputcharacteristics of the photodetector and realizes the relatively largemagnitude of analog voltage which is essential for accuraterepresentation and processing of the detected reflectance values.

Returning to FIG. 3A, the CPU 30 processes the output of photodetector26 through a peak detector 50 which essentially functions to sample thephotodetector output voltage and hold the highest, i.e., peak, voltagevalue encountered after the detector has been enabled. For U.S.currency, the peak detector is also adapted to define a scaled voltageon the basis of which the pattern borderline on bills is detected. Theoutput of the peak detector 50 is fed to a voltage divider 54 whichlowers the peak voltage down to a scaled voltage V_(S) representing apredefined percentage of this peak value. The voltage V_(S) is basedupon the percentage drop in output voltage of the peak detector as itreflects the transition from the "high" reflectance value resulting fromthe scanning of the unprinted edge portions of a currency bill to therelatively lower "gray" reflectance value resulting when the thinborderline is encountered. Preferably, the scaled voltage V_(S) is setto be about 70-80 percent of the peak voltage.

The scaled voltage V_(S) is supplied to a line detector 56 which is alsoprovided with the incoming instantaneous output of the photodetector 26.The line detector 56 compares the two voltages at its input side andgenerates a signal L_(DET) which normally stays "low" and goes "high"when the edge of the bill is scanned. The signal L_(DET) goes "low" whenthe incoming photodetector output reaches the pre-defined percentage ofthe peak photodetector output up to that point, as represented by thevoltage V_(S). Thus, when the signal L_(DET) goes "low", it is anindication that the borderline of the bill pattern has been detected. Atthis point, the CPU 30 initiates the actual reflectance sampling undercontrol of the encoder 32 (see FIG. 3A) and the desired fixed number ofreflectance samples are obtained as the currency bill moves across theilluminated light strip and is scanned along the central section of itsnarrow dimension.

When master characteristic patterns are being generated, the reflectancesamples resulting from the scanning of one or more genuine bills foreach denomination are loaded into corresponding designated sectionswithin a system memory 60, which is preferably an EPROM. The loading ofsamples is accomplished through a buffered address latch 58, ifnecessary. During currency discrimination, the reflectance valuesresulting from the scanning of a test bill are sequentially compared,under control of the correlation program stored within the memory unit38, with each of the corresponding master characteristic patterns storedwithin the EPROM 60, again through the address latch 58. The procedurefor scanning bills and generating characteristic patterns is describedin U.S. Pat. No. 5,295,196 referred to above and incorporated byreference in its entirety and co-pending U.S. patent application Ser.No. 08/243,807, filed on May 16, 1994 and entitled "Method and Apparatusfor Currency Discrimination."

The optical sensing and correlation technique described in U.S. Pat. No.5,295,196 permits identification of pre-programmed currencydenominations with a high degree of accuracy and is based upon arelatively short processing time for digitizing sampled reflectancevalues and comparing them to the master characteristic patterns. Theapproach is used to scan currency bills, normalize the scanned data andgenerate master patterns in such a way that bill scans during operationhave a direct correspondence between compared sample points in portionsof the bills which possess the most distinguishable printed indicia. Arelatively low number of reflectance samples is required in order to beable to adequately distinguish among several currency denominations.

Now that a single scanhead currency scanner has been described inconnection with scanning U.S. currency, the currency discriminationsystem of the present invention will be described.

First of all, because currencies come in a variety of sizes, sensors areadded to determine the size of a bill to be scanned. These sensors areplaced upstream of the scanheads to be described below. A preferredembodiment of size determining sensors is illustrated in FIG. 4. Twoleading/trailing edge sensors 62 detect the leading and trailing edgesof a bill 64 as it passing along the transport path. These sensors inconjunction with the encoder 32 (FIG. 1) may be used to determine thedimension of the bill along a direction parallel to the scan directionwhich in FIG. 4 is the narrow dimension (or width) of the bill 64.Additionally, two side edge sensors 66 are used to detect the dimensionof a bill 64 transverse to the scan direction which in FIG. 4 is thewide dimension (or length) of the bill 64. While the sensors 62 and 66of FIG. 4 are optical sensors, any means of determining the size of abill may be employed.

Once the size of a bill is determined, the potential identity of thebill is limited to those bills having the same size. Accordingly, thearea to be scanned can be tailored to the area or areas best suited foridentifying the denomination and country of origin of a bill having themeasured dimensions.

Secondly, while the printed indicia on U.S. currency is enclosed withina thin borderline, the sensing of which may serve as a trigger to beginscanning using a wider slit, most currencies of other currency systemssuch as those from other countries do not have such a borderline. Thusthe system described above may be modified to begin scanning relative tothe edge of a bill for currencies lacking such a borderline. Referringto FIG. 5, two leading edge detectors 68 are shown. The detection of theleading edge 69 of a bill 70 by leading edge sensors 68 triggersscanning in an area a given distance away from the leading edge of thebill 70, e.g., D₁ or D₂, which may vary depending upon the preliminaryindication of the identity of a bill based on the dimensions of a bill.Alternatively, the leading edge 69 of a bill may be detected by one ormore of the scanheads (to be described below) in a similar manner asthat described with respect to FIGS. 3A and 3B. Alternatively, thebeginning of scanning may be triggered by positional informationprovided by the encoder 32 of FIG. 1, for example, in conjunction withthe signals provided by sensors 62 of FIG. 4, thus eliminating the needfor leading edge sensors 68.

However, when the initiation of scanning is triggered by the detectionof the leading edge of a bill, the chance that a scanned pattern will beoffset relative to a corresponding master pattern increases. Offsets canresult from the existence of manufacturing tolerances which permit thelocation of printed indicia of a document to vary relative to the edgesof the document. For example, the printed indicia on U.S. bills may varyrelative to the leading edge of a bill by as much as 50 mils which is0.05 inches (1.27 mm). Thus when scanning is triggered relative to theedge of a bill (rather than the detection of a certain part of theprinted indicia itself, such as the printed borderline of U.S. bills), ascanned pattern can be offset from a corresponding master pattern by oneor more samples. Such offsets can lead to erroneous rejections ofgenuine bills due to poor correlation between scanned and masterpatterns. To compensate, overall scanned patterns and master patternscan be shifted relative to each other as illustrated in FIGS. 6A and 6B.More particularly, FIG. 6A illustrates a scanned pattern which is offsetfrom a corresponding master pattern. FIG. 6B illustrates the samepatterns after the scanned pattern is shifted relative to the masterpattern, thereby increasing the correlation between the two patterns.Alternatively, instead of shifting either scanned patterns or masterpatterns, master patterns may be stored in memory corresponding todifferent offset amounts.

Thirdly, while it has been determined that the scanning of the centralarea on the green side of a U.S. bill (see segment S of FIG. 2B)provides sufficiently distinct patterns to enable discrimination amongthe plurality of U.S. denominations, the central area may not besuitable for bills originating in other countries. For example, forbills originating from Country 1, it may be determined that segment S₁(FIG. 5) provides a more preferable area to be scanned, while segment S₂(FIG. 5) is more preferable for bills originating from Country 2.Alternatively, in order to sufficiently discriminate among a given setof bills, it may be necessary to scan bills which are potentially fromsuch set along more than one segment, e.g., scanning a single bill alongboth S₁ and S₂.

To accommodate scanning in areas other than the central portion of abill, multiple scanheads may be positioned next to each other. Apreferred embodiment of such a multiple scanhead system is depicted inFIG. 7. Multiple scanheads 72a-c and 72d-f are positioned next to eachother along a direction lateral to the direction of bill movement. Sucha system permits a bill 74 to be scanned along different segments.Multiple scanheads 72a-f are arranged on each side of the transportpath, thus permitting both sides of a bill 74 to be scanned.

Two-sided scanning may be used to permit bills to be fed into a currencydiscrimination system according to the present invention with eitherside face up. An example of a two-sided scanhead arrangement isdisclosed in co-pending U.S. patent application Ser. No. 08/207,592filed on Mar. 8, 1994 and incorporated herein by reference. Masterpatterns generated by scanning genuine bills may be stored for segmentson one or both sides. In the case where master patterns are stored fromthe scanning of only one side of a genuine bill, the patterns retrievedby scanning both sides of a bill under test may be compared to a masterset of single-sided master patterns. In such a case, a pattern retrievedfrom one side of a bill under test should match one of the stored masterpatterns, while a pattern retrieved from the other side of the billunder test should not match one of the master patterns. Alternatively,master patterns may be stored for both sides of genuine bills. In such atwo-sided system, a pattern retrieved by scanning one side of a billunder test should match with one of the master patterns of one side(Match 1) and a pattern retrieved from scanning the opposite side of abill under test should match the master pattern associated with theopposite side of a genuine bill identified by Match 1.

Alternatively, in situations where the face orientation of a bill (i.e.,whether a bill is "face up" or "face down") may be determined prior toor during characteristic pattern scanning, the number of comparisons maybe reduced by limiting comparisons to patterns corresponding to the sameside of a bill. That is, for example, when it is known that a bill is"face up", scanned patterns associated with scanheads above thetransport path need only be compared to master patterns generated byscanning the "face" of genuine bills. By "face" of a bill it is meant aside which is designated as the front surface of the bill. For example,the front or "face" of a U.S. bill may be designated as the "black"surface while the back of a U.S. bill may be designated as the "green"surface. The face orientation may be determinable in some situations bysensing the color of the surfaces of a bill. An alternative method ofdetermining the face orientation of U.S. bills by detecting theborderline on each side of a bill is disclosed in co-pending U.S. patentapplication Ser. No. 08/207,592 filed on Mar. 8, 1994. Theimplementation of color sensing is discussed in more detailed below.

According to the embodiment of FIG. 7, the bill transport mechanismoperates in such a fashion that the central area C of a bill 74 istransported between central scanheads 72b and 72e. Scanheads 72a and 72cand likewise scanheads 72d and 72f are displaced the same distance fromcentral scanheads 72b and 72e, respectively. By symmetrically arrangingthe scanheads about the central region of a bill, a bill may be scannedin either direction, e.g., top edge first (forward direction) or bottomedge first (reverse direction). As described above with respect to FIGS.1-3, master patterns are stored from the scanning of genuine bills inboth the forward and reverse directions. While a symmetrical arrangementis preferred, it is not essential provided appropriate master patternsare stored for a non-symmetrical system.

While FIG. 7 illustrates a system having three scanheads per side, anynumber of scanheads per side may be utilized. Likewise, it is notnecessary that there be a scanhead positioned over the central region ofa bill. For example, FIG. 8 illustrates another preferred embodiment ofthe present invention capable of scanning the segments S₁ and S₂ of FIG.5. Scanheads 76a, 76d, 76e, and 76h scan a bill 78 along segment S₁while scanheads 76b, 76c, 76f, and 76g scan segment S₂.

FIG. 9 depicts another preferred embodiment of a scanning systemaccording to the present invention having laterally moveable scanheads80a-b. Similar scanheads may be positioned on the opposite side of thetransport path. Moveable scanheads 80a-b may provide more flexibilitythat may be desirable in certain scanning situations. Upon thedetermination of the dimensions of a bill as described in connectionwith FIG. 4, a preliminary determination of the identity of a bill maybe made. Based on this preliminary determination, the moveable scanheads80a-b may be positioned over the area of the bill which is mostappropriate for retrieving discrimination information. For example, ifbased on the size of a scanned bill, it is preliminarily determined thatthe bill is a Japanese 5000 Yen bill-type, and if it has been determinedthat a suitable characteristic pattern for a 5000 Yen bill-type isobtained by scanning a segment 2.0 cm to the left of center of the billfed in the forward direction, scanheads 80a and 80b may be appropriatelypositioned for scanning such a segment, e.g., scanhead 80a positioned2.0 cm left of center and scanhead 80b positioned 2.0 cm right ofcenter. Such positioning permits proper discrimination regardless of thewhether the scanned bill is being fed in the forward or reversedirection. Likewise scanheads on the opposite side of the transport path(not shown) could be appropriately positioned. Alternatively, a singlemoveable scanhead may be used on one or both sides of the transportpath. In such a system, size and color information (to be described inmore detail below) may be used to properly position a single laterallymoveable scanhead, especially where the orientation of a bill may bedetermined before scanning.

FIG. 9, depicts a system in which the transport mechanism is designed todeliver a bill 82 to be scanned centered within the area in whichscanheads 80a-b are located. Accordingly, scanheads 80a-b are designedto move relative to the center of the transport path with scanhead 80abeing moveable within the range R₁ and scanhead 80b being moveablewithin range R₂.

FIG. 10 depicts another preferred embodiment of a scanning systemaccording to the present invention wherein bills to be scanned aretransported in a left justified manner along the transport path, that iswherein the left edge L of a bill 84 is positioned in the same laterallocation relative to the transport path. Based on the dimensions of thebill, the position of the center of the bill may be determined and thescanheads 86a-b may in turn be positioned accordingly. As depicted inFIG. 10, scanhead 86a has a range of motion R₃ and scanhead 86b has arange of motion R₄. The ranges of motion of scanheads 86a-b may beinfluenced by the range of dimensions of bills which the discriminationsystem is designed to accommodate. Similar scanheads may be positionedon the opposite side of the transport path.

Alternatively, the transport mechanism may be designed such that scannedbills are not necessarily centered or justified along the lateraldimension of the transport path. Rather the design of the transportmechanism may permit the position of bills to vary left and right withinthe lateral dimension of the transport path. In such a case, the edgesensors 66 of FIG. 4 may be used to locate the edges and center of abill, and thus provide positional information in a moveable scanheadsystem and selection criteria in a stationary scanhead system.

In addition to the stationary scanhead and moveable scanhead systemsdescribed above, a hybrid system having both stationary and moveablescanheads may be used. Likewise, it should be noted that the laterallydisplaced scanheads described above need not lie along the same lateralaxis. That is, the scanheads may be, for example, staggered upstream anddownstream from each other. FIG. 11 is a top view of a staggeredscanhead arrangement according to a preferred embodiment of the presentinvention. As illustrated in FIG. 11, a bill 130 is transported in acentered manner along the transport path 132 so that the center 134 ofthe bill 130 is aligned with the center 136 of the transport path 132.Scanheads 140a-h are arranged in a staggered manner so as to permitscanning of the entire width of the transport path 132. The areasilluminated by each scanhead are illustrated by strips 142a, 142b, 142e,and 142f for scanheads 140a, 140b, 140e, and 140f, respectively. Basedon size determination sensors, scanheads 140a and 140h may either not beactivated or their output ignored.

In general, if prior to scanning a document, preliminary informationabout a document can be obtained, such as its size or color,appropriately positioned stationary scanheads may be activated orlaterally moveable scanheads may be appropriately positioned providedthe preliminary information provides some indication as to the potentialidentity of the document. Alternatively, especially in systems havingscanheads positioned over a significant portion of the transport path,many or all of the scanheads of a system may be activated to scan adocument. Then subsequently, after some preliminary determination as toa document's identity has been made, only the output or derivationsthereof of appropriately located scanheads may be used to generatescanned patterns. Derivations of output signals include, for example,data samples stored in memory generated by sampling output signals.Under such an alternative embodiment, information enabling a preliminarydetermination as to a document's identity may be obtained by analyzinginformation either from sensors separate from the scanheads or from oneor more of the scanheads themselves. An advantage of such preliminarydeterminations is that the number of scanned patterns which have to begenerated or compared to a set of master patterns is reduced. Likewisethe number of master patterns to which scanned patterns must be comparedmay also be reduced.

While the scanheads 140a-h of FIG. 11 are arranged in a non-overlappingmanner, they may alternatively be arranged in an overlapping manner. Byproviding additional lateral positions, an overlapping scanheadarrangement may provide greater selectivity in the segments to bescanned. This increase in scanable segments may be beneficial incompensating for currency manufacturing tolerances which result inpositional variances of the printed indicia on bills relative to theiredges. Additionally, in a preferred embodiment, scanheads positionedabove the transport path are positioned upstream relative to theircorresponding scanheads positioned below the transport path.

FIGS. 12A and 12B illustrate another preferred embodiment of the presentin invention wherein a plurality of analog sensors 150 such asphotodetectors are laterally displaced from each other and are arrangedin a linear array within a single scanhead 152. FIG. 12A is a top viewwhile FIG. 12B is a side elevation view of such a linear arrayembodiment. The output of individual sensors 150 are connected toanalog-to-digital converters (not shown) through the use of graded indexfibers, such as a "lens array" manufactured by MSG America, Inc., partnumber SLA20A1675702A3, and subsequently to a CPU (not shown) in amanner similar to that depicted in FIGS. 1 and 3A. As depicted in FIGS.12A and 12B, a bill 154 is transported past the linear array scanhead152 in a centered fashion. A preferred length for the linear arrayscanhead is about 6-7 inches (15 cm-17 cm).

In a manner similar to that described above, based on the determinationof the size of a bill, appropriate sensors may be activated and theiroutput used to generate scanned patterns. Alternatively many or all ofthe sensors may be activated with only the output or derivations thereofof appropriately located sensors being used to generate scannedpatterns. Derivations of output signals include, for example, datasamples stored in memory generated by sampling output signals. As aresult, a discriminating system incorporating a linear array scanheadaccording the present invention would be capable of accommodating a widevariety of bill-types. Additionally, a linear array scanhead provides agreat deal of flexibility in how information may be read and processedwith respect to various bills. In addition to the ability to generatescanned patterns along segments in a direction parallel to the directionof bill movement, by appropriately processing scanned samples, scannedpatterns may be "generated" or approximated in a direction perpendicularto the direction of bill movement. For example, if the linear arrayscanhead 152 comprises one hundred and sixty (160) sensors 150 over alength of 7 inches (17.78 cm) instead of taking samples for 64 encoderpulses from say 30 sensors, samples may be taken for 5 encoder pulsesfrom all 160 cells (or all those positioned over the bill 154).Alternatively, 160 scanned patterns (or selected ones thereof) of 5 datasamples each may be used for pattern comparisons. Accordingly, it can beseen that the data acquisition time is significantly reduced from 64encoder pulses to only 5 encoder pulses. The time saved in acquiringdata can be used to permit more time to be spent processing data and/orto reduce the total scanning time per bill thus enabling increasedthroughput of the identification system. Additionally, the linear arrayscanhead permits a great deal of flexibility in tailoring the areas tobe scanned. For example, it has been found that the leading edge ofCanadian bills contain valuable graphic information. Accordingly, whenit is determined that a test bill may be a Canadian bill (or when theidentification system is set to a Canadian currency setting), thescanning area can be limited to the leading edge area of bills, forexample, by activating many laterally displaced sensors for a relativelyfew number of encoder pulses.

FIG. 13 is a top view of another preferred embodiment of a linear arrayscanhead 170 having a plurality of analog sensors 172 such asphotodetectors wherein a bill 174 is transported past the scanhead 170in a non-centered manner. As discussed above, positional informationfrom size determining sensors may be used to select appropriate sensors.Alternatively, the linear array scanhead itself may be employed todetermine the size of a bill, thus eliminating the need for separatesize determining sensors. For example, all sensors may be activated,data samples derived from sensors located on the ends of the lineararray scanhead may be preliminarily processed to determine the lateralposition and the length of a bill. The width of a bill may be determinedeither by employing separate leading/trailing edge sensors orpre-processing data samples derived from initial and ending cycleencoder pulses. Once size information is obtained about a bill undertest, only the data samples retrieved from appropriate areas of a billneed be further processed.

FIG. 14 is a top view of another preferred embodiment of a linearscanhead 180 according to the present invention illustrating the abilityto compensate for skewing of bills. Scanhead 180 has a plurality ofanalog sensors 182 and a bill 184 is transported past scanhead 180 in askewed manner. Once the skew of a bill has been determined, for examplethrough the use of leading edge sensors, readings from sensors 182 alongthe scanhead 180 may be appropriately delayed. For example, suppose itis determined that a bill is being fed past scanhead 180 so that theleft front corner of the bill reaches the scanhead five encoder pulsesbefore the right front corner of the bill. In such a case, sensorreadings along the right edge of the bill can be delayed for 5 encoderpulses to compensate for the skew. Where scanned patterns are to begenerated over only a few encoder pulses, the bill may be treated asbeing fed in a non-skewed manner since the amount of lateral deviationbetween a scan along a skewed angle and a scan along a non-skewed angleis minimal for a scan of only a few encoder pulses. However, where it isdesired to obtain a scan over a large number of encoder pulses, a singlescanned pattern may be generated from the outputs of more than onesensor. For example, a scanned pattern may be generated by taking datasamples from sensor 186a for a given number of encoder pulses, thentaking data samples from sensor 186b for a next given number of encoderpulses, and then taking data samples from sensor 186c for a next givennumber of encoder pulses. The number of given encoder pulses for whichdata samples may be taken from the same sensor is influenced by thedegree of skew, the greater the degree of skew of the bill, the fewerthe number of data samples which may be obtained before switching to thenext sensor. Alternatively, master patterns may be generated and storedfor various degrees of skew, thus permitting a single sensor to generatea scanned pattern from a bill under test.

With regards to FIGS. 12-14, while only a single linear array scanheadis shown, another linear array scanhead may be positioned on theopposite side of the transport path to permit scanning of either or bothsides of a bill. Likewise, the benefits of using a linear array scanheadmay also be obtainable using a multiple scanhead arrangement which isconfigured appropriately, for example such as depicted in FIG. 11 or alinear arrangement of multiple scanheads.

In addition to size and scanned characteristic patterns, color may alsobe used to discriminate bills. For example, while all U.S. bills areprinted in the same colors, e.g., a green side and a black side, billsfrom other countries often vary in color with the denomination of thebill. For example, a German 50 deutsche mark bill-type is brown in colorwhile a German 100 deutsche mark bill-type is blue in color.Alternatively, color detection may be used to determine the faceorientation of a bill, such as where the color of each side of a billvaries. For example, color detection may be used to determine the faceorientation of U.S. bills by detecting whether or not the "green" sideof a U.S. bill is facing upwards. Separate color sensors may be addedupstream of the scanheads described above. According to such anembodiment, color information may be used in addition to sizeinformation to preliminarily identify a bill. Likewise, colorinformation may be used to determine the face orientation of a billwhich determination may be used to select upper or lower scanheads forscanning a bill accordingly or compare scanned patterns retrieved fromupper scanheads with a set of master patterns generated by scanning acorresponding face while the scanned patterns retrieved from the lowerscanheads are compared with a set of master patterns generated byscanning an opposing face. Alternatively, color sensing may beincorporated into the scanheads described above. Such color sensing maybe achieved by, for example, incorporating color filters, colored lightsources, and/or dichroic beamsplitters into the currency discriminationsystem of the present invention. Color information acquisition isdescribed in more detail in co-pending U.S. application Ser. No.08/219,093 filed Mar. 29, 1994, for a "Currency Discriminator andAuthenticator" incorporated herein by reference. Various colorinformation acquisition techniques are described in U.S. Pat. Nos.4,841,358; 4,658,289; 4,716,456; 4,825,246; and 4,992,860.

The operation of a currency discriminator according to a preferredembodiment of the present invention may be further understood byreferring to the flowchart of FIGS. 15A and 15B. In the processbeginning at step 100, a bill is fed along a transport path (step 102)past sensors which measure the length and width of the bill (step 104).These size determining sensors may be, for example, those illustrated inFIG. 4. Next at step 106, it is determined whether the measureddimensions of the bill match the dimensions of at least one bill storedin memory, such as EPROM 60 of FIG. 3. If no match is found, anappropriate error is generated at step 108. If a match is found, thecolor of the bill is scanned for at step 110. At step 112, it isdetermined whether the color of the bill matches a color associated witha genuine bill having the dimensions measured at step 104. An error isgenerated at step 114 if no such match is found. However, if a match isfound, a preliminary set of potentially matching bills is generated atstep 116. Often, only one possible identity will exist for a bill havinga given color and dimensions. However, the preliminary set of step 116is not limited to the identification of a single bill-type, that is, aspecific denomination of a specific currency system; but rather, thepreliminary set may comprise a number of potential bill-types. Forexample, all U.S. bills have the same size and color. Therefore, thepreliminary set generated by scanning a U.S. $5 bill would include U.S.bills of all denominations.

Based on the preliminary set (step 116), selected scanheads in astationary scanhead system may be activated (step 118). For example, ifthe preliminary identification indicates that a bill being scanned hasthe color and dimensions of a German 100 deutsche mark, the scanheadsover regions associated with the scanning of an appropriate segment fora German 100 deutsche mark may be activated. Then upon detection of theleading edge of the bill by sensors 68 of FIG. 5, the appropriatesegment may be scanned. Alternatively, all scanheads may be active withonly the scanning information from selected scanheads being processed.Alternatively, based on the preliminary identification of a bill (step116), moveable scanheads may be appropriately positioned (step 118).

Subsequently, the bill is scanned for a characteristic pattern (step120). At step 122, the scanned patterns produced by the scanheads arecompared with the stored master patterns associated with genuine billsas dictated by the preliminary set. By only making comparisons withmaster patterns of bills within the preliminary set, processing time maybe reduced. Thus for example, if the preliminary set indicated that thescanned bill could only possibly be a German 100 deutsche mark, thenonly the master pattern or patterns associated with a German 100deutsche mark need be compared to the scanned patterns. If no match isfound, an appropriate error is generated (step 124). If a scannedpattern does match an appropriate master pattern, the identity of thebill is accordingly indicated (step 126) and the process is ended (step128).

While some of the preferred embodiments discussed above entailed asystem capable of identifying a plurality of bill-types, the system maybe adapted to identify a bill under test as either belonging to aspecific bill-type or not. For example, the system may be adapted tostore master information associated with only a single bill-type such asa United Kingdom 5 pound bill. Such a system would identify bills undertest which were United Kingdom 5 pound bills and would reject all otherbill-types.

The scanheads of the present invention may be incorporated into adocument identification system capable of identifying a variety ofdocuments. For example, the system may be designed to accommodate anumber of currencies from different countries. Such a system may bedesigned to permit operation in a number of modes. For example, thesystem may be designed to permit an operator to select one or more of aplurality of bill-types which the system is designed to accommodate.Such a selection may be used to limit the number of master patterns withwhich scanned patterns are to be compared. Likewise, the operator may bepermitted to select the manner in which bills will be fed, such as allbills face up, all bills top edge first, random face orientation, and/orrandom top edge orientation. Additionally, the system may be designed topermit output information to be displayed in a variety of formats to avariety of peripherals, such as a monitor, LCD display, or printer. Forexample, the system may be designed to count the number of each specificbill-types identified and to tabulate the total amount of currencycounted for each of a plurality of currency systems. For example, astack of bills could be placed in the bill accepting station 12 of FIG.1, and the output unit 36 of FIG. 1 may indicate that a total of 370British pounds and 650 German marks were counted. Alternatively, theoutput from scanning the same batch of bills may provide more detailedinformation about the specific denominations counted, for example one100 pound bill, five 50 pound bills, and one 20 pound bill and thirteen50 deutsche mark bills.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and herein described in detail. It should beunderstood, however, that it is not intended to limit the invention tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

We claim:
 1. A currency identification system comprising:a billtransport mechanism for transporting a currency bill to be scanned alonga transport path; at least two scanheads positioned on a first side ofsaid transport path so as to permit scanning of said bill along at leasttwo segments, said scanheads being capable of detecting characteristicinformation from said bill along said segments and generatingcorresponding output signals representing variations in the detectedcharacteristic information from which scanned patterns of characteristicinformation may be generated, at least two of said scanheads beinglaterally displaced relative to each other; means for choosing at leastone of said scanheads for scanning said bill along at least one segmentbased on a preliminary determination of the identity of said bill; meansfor generating at least one scanned pattern from said output signals,said at least one scanned pattern representing analog variations in saidcharacteristic information along a segment of said bill; a memory forstoring at least one master pattern associated with each genuine billwhich the system is capable of identifying, said at least one masterpattern representing analog variations in characteristic informationalong a segment of an associated genuine bill; and a signal processingmeans for performing a pattern comparison wherein at least one of saidscanned patterns or portions thereof is compared with at least one ofsaid master patterns or portions thereof; said signal processing meansgenerating an indication of the identity of said bill based on saidpattern comparison when said bill is one that the system is capable ofidentifying.
 2. The currency identification system of claim 1 wherein atleast two of said scanheads are stationary scanheads.
 3. The currencyidentification system of claim 1 wherein at least two of said scanheadsare laterally moveable scanheads.
 4. The currency identification systemof claim 3 wherein said moveable scanheads are laterally positionedbased upon said preliminary determination of the identity of said bill.5. The currency identification system of claim 1wherein at least two ofsaid scanheads are optical scanheads; wherein said optical scanheadseach include at least one light source for illuminating a strip of saidsegments of said bill, and at least one detector for receiving reflectedlight from a corresponding illuminated strip on said bill; wherein saidoutput signals represent variations in the intensity of reflected light;wherein said means for generating at least one scanned pattern from saidoutput signals comprises means for sampling said output signals atpreselected intervals as said bill is moved past a correspondingscanhead, each of said output signal samples being proportional to theintensity of the light reflected from a different strip of acorresponding segment; and wherein said at least one master pattern is amaster pattern of reflected light intensity signal samples.
 6. Thecurrency identification system of claim 1 further comprising:at leasttwo scanheads positioned on a second side of said transport path so asto permit scanning of said bill along at least two segments, saidsecond-side scanheads being capable of detecting characteristicinformation from said bill along said segments and generatingcorresponding output signals representing variations in the detectedcharacteristic information from which scanned patterns of characteristicinformation may be generated, at least two of said second-side scanheadsbeing laterally displaced relative to each other.
 7. The currencyidentification system of claim 1 further comprising:a size detectionsensor for retrieving size information from said bill; a memory forstoring master size information associated with genuine bills which thesystem is capable of identifying; and signal processing means forperforming a size comparison wherein said size information of said billis compared with master size information associated with at least one ofthe genuine bills which the system is capable of identifying and whereinsaid preliminary determination of the identity of said bill is based onsaid size comparison.
 8. The currency identification system of claim 1further comprising:a color detection sensor for retrieving colorinformation from said bill; a memory for storing master colorinformation associated with genuine bills which the system is capable ofidentifying; and signal processing means for performing a colorcomparison wherein said color information of said bill is compared withmaster color information associated with at least one of the genuinebills which the system is capable of identifying and wherein saidpreliminary determination of the identity of said bill is based on saidcolor comparison.
 9. The currency identification system of claim 1wherein said means for choosing selects at least one of said scanheadsfor scanning said bill along at least one segment based on a preliminarydetermination of the identity of said bill.
 10. The currencyidentification system of claim 1 wherein said means for choosingactivates at least one of said scanheads for scanning said bill along atleast one segment based on a preliminary determination of the identityof said bill.
 11. A currency identification system comprising:a billtransport mechanism for transporting a currency bill to be scanned alonga transport path; one or more laterally moveable analog scanheadspositioned on a first side of said transport path so as to permitscanning of said bill along at least one segment, said scanhead beingcapable of detecting characteristic information from said bill alongsaid segment and generating corresponding output signal representingvariations in the detected characteristic information from which scannedpatterns of characteristic information may be generated; means forgenerating at least one scanned pattern from said output signal, said atleast one scanned pattern representing analog variations in saidcharacteristic information along a segment of said bill; a memory forstoring at least one master pattern associated with each genuine billwhich the system is capable of identifying, said at least one masterpattern representing analog variations in characteristic informationalong a segment of an associated genuine bill; and a signal processingmeans for performing a pattern comparison wherein at least one of saidscanned patterns or portions thereof is compared with at least one ofsaid master patterns or portions thereof; said signal processing meansgenerating an indication of the identity of said bill based on saidpattern comparison when said bill is one that the system is capable ofidentifying.
 12. The currency identification system of claim 11whereinat least one of said scanheads is an optical scanhead; wherein saidoptical scanhead includes at least one light source for illuminating astrip of said segments of said bill, and at least one detector forreceiving reflected light from a corresponding illuminated strip on saidbill; wherein said output signals represent variations in the intensityof reflected light; wherein said means for generating at least onescanned pattern from said output signal comprises means for samplingsaid output signal at preselected intervals as said bill is moved past acorresponding scanhead, each of said output signal samples beingproportional to the intensity of the light reflected from a differentstrip of a corresponding segment; and wherein said at least one masterpattern is a master pattern of reflected light intensity signal samples.13. The currency identification system of claim 11 furthercomprising:one or more laterally moveable analog scanheads positioned ona second side of said transport path so as to permit scanning of saidbill along at least one segment, said second-side scanhead being capableof detecting characteristic information from said bill along saidsegment and generating corresponding output signal representingvariations in the detected characteristic information from which scannedpatterns of characteristic information may be generated.
 14. Thecurrency identification system of claim 11 further comprising:a sizedetection sensor for retrieving size information from said bill; amemory for storing master size information associated with said genuinebills which the system is capable of identifying; and signal processingmeans for performing a size comparison wherein said size information ofsaid bill is compared with master size information associated with atleast one of the genuine bills which the system is capable ofidentifying and wherein said identification indication is additionallybased on said size comparison.
 15. The currency identification system ofclaim 11 further comprising:a color detection sensor for retrievingcolor information from said bill; a memory for storing master colorinformation associated with said genuine bills which the system iscapable of identifying; and signal processing means for performing acolor comparison wherein said color information of said bill is comparedwith master color information associated with at least one of thegenuine bills which the system is capable of identifying and whereinsaid identification indication is additionally based on said colorcomparison.
 16. The currency identification system of claim 11 whereinsaid moveable scanheads are laterally positioned based upon apreliminary determination of the identity of said bill.
 17. The currencyidentification system of claim 11 wherein at least two of said scanheadsare laterally moveable scanheads.
 18. A currency identification systemcomprising:a linear array scanhead comprising at least three laterallydisplaced sensors positioned so as to permit scanning along at leastthree laterally displaced segments on a first side of a bill, saidsensors being capable of detecting characteristic information from saidbill along said segments and generating corresponding output signalsrepresenting variations in the detected characteristic information fromwhich scanned patterns of characteristic information may be generated,said scanhead being able to scan at a rate in excess of about 800 billsper minute; means for generating at least three scanned patterns fromsaid output signals, said at least three scanned patterns representingand approximating analog variations in said characteristic informationalong segments of said bill; a memory for storing at least three masterpatterns associated with each genuine bill which the system is capableof identifying, said at least three master patterns representing andapproximating analog variations in characteristic information alongsegments of an associated genuine bill; and a signal processing meansfor performing a pattern comparison wherein at least one of said scannedpatterns or portions thereof is compared with at least one of saidmaster patterns or portions thereof; said signal processing meansdetermining the denomination of said bill based on said patterncomparison when said bill is one that the system is capable ofidentifying.
 19. The currency identification system of claim 18 whereinsaid sensors are analog sensors.
 20. The currency identification systemof claim 18wherein at least two of said linear array sensors are opticalsensors; wherein said linear array scanhead includes at least one lightsource for illuminating a strip of said segments of said bill, saidlinear array sensors receiving reflected light from said illuminatedstrip on said bill; wherein said output signals represent variations inthe intensity of reflected light; wherein said means for generating atleast one scanned pattern from said output signals comprises means forsampling said output signals at preselected intervals as said bill ismoved past a corresponding linear array sensor, each of said outputsignal samples being proportional to the intensity of the lightreflected from a different strip of a corresponding segment; and whereinsaid at least one master pattern is a master pattern of reflected lightintensity signal samples.
 21. The currency identification system ofclaim 18 further comprising:a second linear array scanhead comprising atleast two sensors positioned so as to permit scanning along at least twosegments on a second side of said bill, said second-side sensors beingcapable of detecting characteristic information from said bill alongsaid second-side segments and generating corresponding output signalsrepresenting variations in the detected characteristic information fromwhich scanned patterns of characteristic information may be generated,at least two of said second-side sensors being laterally displacedrelative to each other.
 22. The currency identification system of claim18 further comprising:a size detection sensor for retrieving sizeinformation from said bill; a memory for storing master size informationassociated with genuine bills which the system is capable ofidentifying; and signal processing means for performing a sizecomparison wherein said size information of said bill is compared withmaster size information associated with at least one of the genuinebills which the system is capable of identifying and wherein saididentity indication is additionally based on said size comparison. 23.The currency identification system of claim 22 wherein said sizedetection sensor is positioned upstream from said scanhead; wherein saidsize comparison is performed before said bill is scanned by said lineararray sensors; and wherein one or more of said linear array sensors areselected to scan said bill based on said size comparison.
 24. Thecurrency identification system of claim 23 wherein said signalprocessing means generates a preliminary set of potentially matchingbills for said bill based on said size comparison and wherein said atleast one of said master patterns of said pattern comparison is chosenfrom said preliminary set.
 25. The currency identification system ofclaim 23wherein said linear array sensors are optical sensors; whereinsaid linear array scanhead includes at least one light source forilluminating a strip of said segments of said bill, said linear arraysensors receiving reflected light from said illuminated strip on saidbill; wherein said output signals represent variations in the intensityof reflected light; wherein said means for generating at least onescanned pattern from said output signals comprises means for samplingsaid output signals at preselected intervals as said bill is moved pasta corresponding linear array sensor, each of said output signal samplesbeing proportional to the intensity of the light reflected from adifferent strip of a corresponding segment; and wherein said at leastone master pattern is a master pattern of reflected light intensitysignal samples.
 26. The currency identification system of claim 22wherein said size detection sensor is positioned upstream from saidscanhead; wherein said size comparison is performed before said bill isscanned by said linear array sensors; and wherein the output signalsfrom one or more of said linear array sensors or derivations thereof areselected for the generation of scanned patterns based on said sizecomparison.
 27. The currency identification system of claim 18 furthercomprising:a color detection sensor for retrieving color informationfrom said bill; a memory for storing master color information associatedwith genuine bills which the system is capable of identifying; andsignal processing means for performing a color comparison wherein saidcolor information of said bill is compared with master color informationassociated with at least one of the genuine bills which the system iscapable of identifying and wherein said identity indication isadditionally based on said color comparison.
 28. The currencyidentification system of claim 27 wherein said color detection sensor ispositioned upstream from said scanhead; wherein said color comparison isperformed before said bill is scanned by said linear array sensors; andwherein one or more of said linear array sensors are selected to scansaid bill based on said color comparison.
 29. The currencyidentification system of claim 28 wherein said signal processing meansgenerates a preliminary set of potentially matching bills for said billbased on said color comparison and wherein said at least one of saidmaster patterns of said pattern comparison is chosen from saidpreliminary set.
 30. The currency identification system of claim28wherein said linear array sensors are optical sensors; wherein saidlinear array scanhead includes at least one light source forilluminating a strip of said segments of said bill, said linear arraysensors receiving reflected light from said illuminated strip on saidbill; wherein said output signals represent variations in the intensityof reflected light; wherein said means for generating at least onescanned pattern from said output signals comprises means for samplingsaid output signals at preselected intervals as said bill is moved pasta corresponding linear array sensor, each of said output signal samplesbeing proportional to the intensity of the light reflected from adifferent strip of a corresponding segment; and wherein said at leastone master pattern is a master pattern of reflected light intensitysignal samples.
 31. The currency identification system of claim 27wherein said color detection sensor is positioned upstream from saidscanhead; wherein said color comparison is performed before said bill isscanned by said linear array sensors; and wherein the output signalsfrom one or more of said linear array sensors or derivations thereof areselected for the generation of scanned patterns based on said colorcomparison.
 32. The currency identification system of claim 18 whereinthe lateral positioning of said bill relative to said scanhead isdetermined before said bill passes said scanhead and wherein one or moreof said linear array sensors are selected to scan said bill based onsaid lateral positioning determination.
 33. The currency identificationsystem of claim 18 wherein all of the linear array sensors of saidlinear array scanhead are activated; wherein the lateral positioning ofsaid bill relative to said scanhead is determined by analyzing theoutput signals of the outermost linear array sensors or derivationsthereof; and the output signals from one or more of said linear arraysensors or derivations thereof are selected for the generation ofscanned patterns based on said lateral positioning determination. 34.The currency identification system of claim 18 wherein all of the lineararray sensors of said linear array scanhead are activated; wherein thelateral dimension of said bill is determined by analyzing the outputsignals of the outermost linear array sensors or derivations thereof;and the output signals from one or more of said linear array sensors orderivations thereof are selected for the generation of scanned patternsbased on said lateral dimension determination.
 35. The currencyidentification system of claim 18 wherein the dimension of said billparallel to the direction of bill movement is determined by analyzingthe output signals of one or more of said linear array sensors orderivations thereof.
 36. The currency identification system of claim 18wherein the skew of said bill is determined by analyzing the outputsignals of one or more of said linear array sensors or derivationsthereof.
 37. The currency identification system of claim 18 wherein theoutput signals from one or more of said linear array sensors orderivations thereof are selected for the generation of scanned patternsbased on a determination of the skew of said bill.
 38. The currencyidentification system of claim 37 wherein a scanned pattern is generatedfrom the output signal of two or more of said linear array sensors orderivations thereof.
 39. The currency identification system of claim 18wherein said bill is transported along a transport path in a skewedmanner and wherein the generation of a scanned pattern from a givensensor is delayed by an amount related to the angle of skewing of saidbill and the lateral position of said given sensor.
 40. The currencyidentification system of claim 18 wherein the lateral positioning ofsaid bill relative to said scanhead is determined before said billpasses said scanhead and wherein one or more of said linear arraysensors are selected to scan said bill based on said lateral positioningdetermination or the output signals from one or more of said lineararray sensors or derivations thereof are selected for the generation ofscanned patterns based on said lateral positioning determination.
 41. Acurrency identification system comprising:a bill transport mechanism fortransporting a currency bill to be scanned along a transport path at arate in excess of about 800 bills per minute; a linear array scanheadcomprising at least two sensors positioned on a first side of saidtransport path so as to permit scanning of said bill along at least twosegments, said scanheads being capable of detecting characteristicinformation from said bill along said segments and generatingcorresponding output signals representing variations in the detectedcharacteristic information from which scanned patterns of characteristicinformation may be generated, at least two of said sensors beinglaterally displaced relative to each other; means for choosing at leastone of said scanheads for scanning said bill along at least one segmentbased on a preliminary determination of the identity of said bill; meansfor generating at least one scanned pattern from said output signals,said at least one scanned pattern representing analog variations in saidcharacteristic information along a segment of said bill; a memory forstoring at least one master pattern associated with each genuine billwhich the system is capable of identifying, said at least one masterpattern representing analog variations in characteristic informationalong a segment of an associated genuine bill; and a signal processingmeans for performing a pattern comparison wherein at least one of saidscanned patterns or portions thereof is compared with at least one ofsaid master patterns or portions thereof; said signal processing meansgenerating an indication of the identity of said bill based on saidpattern comparison when said bill is one that the system is capable ofidentifying.
 42. The currency identification system of claim 41 whereinsaid means for choosing selects at least one of said scanheads forscanning said bill along at least one segment based on a preliminarydetermination of the identity of said bill.
 43. The currencyidentification system of claim 41 wherein said means for choosingactivates at least one of said scanheads for scanning said bill along atleast one segment based on a preliminary determination of the identityof said bill.
 44. A document identification system comprising:a lineararray scanhead comprising at least three laterally displaced sensorspositioned so as to permit scanning along at least three laterallydisplaced segments on a first side of a document, said sensors beingcapable of detecting characteristic information from said document alongsaid segments and generating corresponding output signals representingvariations in the detected characteristic information from which scannedpatterns of characteristic information may be generated, said scanheadbeing able to scan at a rate in excess of about 800 documents perminute; means for generating at least three scanned patterns from saidoutput signals, said at least three scanned patterns representing andapproximating analog variations in said characteristic information alongsegments of said document; a memory for storing at least three masterpatterns associated with each genuine document which the system iscapable of identifying, said at least three master patterns representingand approximating analog variations in characteristic information alongsegments of an associated genuine document; and a signal processingmeans for performing a pattern comparison wherein at least one of saidscanned patterns or portions thereof is compared with at least one ofsaid master patterns or portions thereof; said signal processing meansdetermining the denomination of said document based on said patterncomparison when said document is one that the system is capable ofidentifying.
 45. An improved method for identifying currency bills in acurrency identification system, the system being capable of identifyingbills that are of one or more bill-types, comprising the stepsof:scanning a test bill along at least three laterally displacedsegments located on a first side of said test bill for variations incharacteristic information along said segments, said scanning beingperformed by at least three laterally displaced analog first-sidesensors at a rate in excess of about 800 bills per minute; generating anoutput signal from at least three of said sensors; generating at leastthree scanned patterns from said output signals, said at least threescanned patterns representing and approximating analog variations insaid characteristic information along segments of said bill; performinga pattern comparison wherein at least one of said scanned patterns orportions thereof is compared with one or more master patterns orportions thereof from a set of master patterns, said master patternsbeing associated with genuine bills of the bill-types that the system iscapable of identifying, said master patterns representing andapproximating analog variations in characteristic information alongsegments of an associated genuine bill; and determining the denominationof said test bill based on said pattern comparison when said test billis one that the system is capable of identifying.
 46. An improved methodfor identifying documents in a document identification system, thesystem being capable of identifying documents that are of one or moredocument-types, comprising the steps of:scanning a test document alongat least three laterally displaced segments located on a first side ofsaid test document for variations in characteristic information alongsaid segments, said scanning being performed by at least three laterallydisplaced analog first-side sensors at a rate in excess of about 800documents per minute; generating an output signal from at least three ofsaid sensors; generating at least three scanned patterns from saidoutput signals, said at least three scanned patterns representing andapproximating analog variations in said characteristic information alongsegments of said document; performing a pattern comparison wherein atleast one of said scanned patterns or portions thereof is compared withone or more master patterns or portions thereof from a set of masterpatterns, said master patterns being associated with genuine documentsof the document-types that the system is capable of identifying, saidmaster patterns representing and approximating analog variations incharacteristic information along segments of an associated genuinedocument; and determining the denomination of said test document basedon said pattern comparison when said test document is of a document-typethat the system is capable of identifying.
 47. A currency identificationsystem comprising:a bill transport mechanism for transporting a currencybill to be scanned along a transport path; at least two scanheadspositioned on a first side of said transport path so as to permitscanning of said bill along at least two segments, said scanheads beingcapable of detecting characteristic information from said bill alongsaid segments and generating corresponding output signals representingvariations in the detected characteristic information from which scannedpatterns of characteristic information may be generated, at least two ofsaid scanheads being laterally displaced relative to each other; meansfor selecting at least one of said output signals for the generation ofscanned patterns based on a preliminary determination of the identity ofsaid bill; means for generating at least one scanned pattern from saidoutput signals, said at least one scanned pattern representing analogvariations in said characteristic information along a segment of saidbill; a memory for storing at least one master pattern associated witheach genuine bill which the system is capable of identifying, said atleast one master pattern representing analog variations incharacteristic information along a segment of an associated genuinebill; and a signal processing means for performing a pattern comparisonwherein at least one of said scanned patterns or portions thereof iscompared with at least one of said master patterns or portions thereof;said signal processing means generating an indication of the identity ofsaid bill based on said pattern comparison when said bill is one thatthe system is capable of identifying.
 48. The currency identificationsystem of claim 47 wherein at least two of said scanheads are stationaryscanheads.
 49. The currency identification system of claim 47 wherein atleast two of said scanheads are laterally moveable scanheads.
 50. Thecurrency identification system of claim 49 wherein said moveablescanheads are laterally positioned based upon said preliminarydetermination of the identity of said bill.
 51. The currencyidentification system of claim 47wherein at least two of said scanheadsare optical scanheads; wherein said optical scanheads each include atleast one light source for illuminating a strip of said segments of saidbill, and at least one detector for receiving reflected light from acorresponding illuminated strip on said bill; wherein said outputsignals represent variations in the intensity of reflected light;wherein said means for generating at least one scanned pattern from saidoutput signals comprises means for sampling said output signals atpreselected intervals as said bill is moved past a correspondingscanhead, each of said output signal samples being proportional to theintensity of the light reflected from a different strip of acorresponding segment; and wherein said at least one master pattern is amaster pattern of reflected light intensity signal samples.
 52. Thecurrency identification system of claim 47 further comprising:at leasttwo scanheads positioned on a second side of said transport path so asto permit scanning of said bill along at least two segments, saidsecond-side scanheads being capable of detecting characteristicinformation from said bill along said segments and generatingcorresponding output signals representing variations in the detectedcharacteristic information from which scanned patterns of characteristicinformation may be generated, at least two of said second-side scanheadsbeing laterally displaced relative to each other.
 53. The currencyidentification system of claim 47 further comprising:a size detectionsensor for retrieving size information from said bill; a memory forstoring master size information associated with genuine bills which thesystem is capable of identifying; and signal processing means forperforming a size comparison wherein said size information of said billis compared with master size information associated with at least one ofthe genuine bills which the system is capable of identifying and whereinsaid preliminary determination of the identity of said bill is based onsaid size comparison.
 54. The currency identification system of claim 47further comprising:a color detection sensor for retrieving colorinformation from said bill; a memory for storing master colorinformation associated with genuine bills which the system is capable ofidentifying; and signal processing means for performing a colorcomparison wherein said color information of said bill is compared withmaster color information associated with at least one of the genuinebills which the system is capable of identifying and wherein saidpreliminary determination of the identity of said bill is based on saidcolor comparison.
 55. A currency identification system comprising:a billtransport mechanism for transporting a currency bill to be scanned alonga transport path at a rate in excess of about 800 bills per minute; alinear array scanhead comprising at least two sensors positioned on afirst side of said transport path so as to permit scanning of said billalong at least two segments, said scanheads being capable of detectingcharacteristic information from said bill along said segments andgenerating corresponding output signals representing variations in thedetected characteristic information from which scanned patterns ofcharacteristic information may be generated, at least two of saidsensors being laterally displaced relative to each other; means forselecting at least one of said output signals for the generation ofscanned patterns based on a preliminary determination of the identity ofsaid bill; means for generating at least one scanned pattern from saidoutput signals, said at least one scanned pattern representing analogvariations in said characteristic information along a segment of saidbill; a memory for storing at least one master pattern associated witheach genuine bill which the system is capable of identifying, said atleast one master pattern representing analog variations incharacteristic information along a segment of an associated genuinebill; and a signal processing means for performing a pattern comparisonwherein at least one of said scanned patterns or portions thereof iscompared with at least one of said master patterns or portions thereof;said signal processing means generating an indication of the identity ofsaid bill based on said pattern comparison when said bill is one thatthe system is capable of identifying.